my lacie big disk extreme & maxtor derive is not work

How are they connected?

OK, Have you Shut down your Mac and disconnected your firewire cable from both ends and let it sit about ten minutes then reconnect and try. Also, it is important to disconnect the AC power to your Mac, this helps to reset the FireWire port(s)

Launch Applications/Utilities/Terminal and copy & paste this command at the prompt:

diskutil list

Press return.

If it sees the disk, please tell us and note the number of the disks (far left column) you want to mount.